The goal of this project is to examine human sexual dimorphism in telencephalic asymmetries in the developing fetal brain, during the first decade of life, and throughout adulthood. There is increasing evidence that the gonadal steroids have a pervasive influence on developing CNS structures involved with both reproductive and non reproductive functions. A first aim is to investigate telencephalic regional volumetric asymmetries in the adult human brain with special reference to sex, handedness and age. Gross morphometric measurements will be taken on 80 adult human brains. Following anatomical labelling, each hemisphere will then be cut in a complete series of 5mm coronal sections in an anterior to posterior sequence. Each section will be photographed and digitized. 5 sets of regional volumes will then be computed using the laboratory software package CARP, macros, or small programs tailored to this purpose, and the SPSSx statistical package. These techniques and methods have been designed to maximize efficiency in handling large quantities of data. A second aim is to investigate sex differences in the development of asymmetries in fetal and juvenile brains. Coronal sections of fetal cerebra from the Yakovlev collection will be used for this purpose. Regional volumes will be computed using the same methods described in the above study. Finally, a third aim is to examine telencephalic sexual dimorphism in cytoarchitectionically defined right and left homologous regions. This work will be done on adult human brains from the Yakovlev collections. Since it has recently been hypothesized that excessive exposure and/or sensitivity to testosterone may induce delayed development of the left hemisphere and that, in turn, delayed left hemisphere development may play a role in learning disabilities, we believe that the proposed work should contribute to our knowledge of abnormal cognitive functions. In addition, research on sexual dimorphism in the brain helps elucidate the relationship between structure and function. We hope, therefore, that results from the proposed research will give us insights into normal human brain function as well as on the neuropsychology of sex differences.